Lalande Crater

Steep walls, riddled with boulders, fields of scree, full of fissures - there are few craters on the Moon like Lalande. This page gets about as nerdy as possible about lunar geography. I bet there is no place else in the solar system (beyond Earth) that has a fan page like this. Prepare for the full nerd treatment.

This is the far north end of a frame taken by the Apollo 16 panoramic camera. Each frame covers a ground area 320 km long and 20 km wide, with the smallest detail recorded being about 2 m across - almost as good as the resolution of the Lunar Reconnaissance Orbiter, whose best images have pixels equal to 50 cm on the ground. The location of 'downtown' Cernan's Promise is indicated.

The anatomy of a crater is really clear here. The rim remains sharp, and all the features clear. It is younger than most lunar craters, but still 2.2 to 2.8 billion years old. The age when the Moon was being battered by meteors all the time had long since ended when the Lalande impact occurred. The way the surrounding ground was raised near the rim, and thickened by a carpet of blast debris, is visible in the slope upwards to the rim extending 3 or 4 km outside the crater. The line where the granular layer of the ground ends and solid bedrock begins is evident where a pretty even, flat slope suddenly switches to a series of scallops and shelves that then descend at a much shallower angle towards the crater floor. The difference is especially dramatic on the south and west walls. The flat crater floor clearly demarks where lava and debris pooled after the blast. The lava was created by the energy of the explosion - the impacting asteroid would have been between 1 and 2 km wide and moving at something like 20 or 30 km/s. The central mountains show where the shockwaves from the blast caused the ground to rebound and well up.

The Apollo 16 service module took 1435 images of the lunar surface during its 3 days in lunar orbit. The image above is from one of two taken of the area during the last orbit recording these photos. It shows about a tenth of the full image. These photos were designed to be combined in pairs to produce a stereoscopic image of the surface - the kind that look 3D when viewed with those red-and-blue glasses. (Yes, i'll do that when i have a chance and figure out how.) The full images from this camera looked like the one below, which is the pair of the image above:

Each of these is a swath showing 12° of latitude and about 1° of longitude. Note how much the perspective changes between the middle and the edges. This is an extreme wide-angle view.

The exposure in the 2nd image of the pair is higher. A lot more detail is visible in the shadows, but the bright areas are washed out. The area of greatest interest is in the shadows of the crater's east wall, that's where the galleries of Cernan's Promise go. So, i got the highest resolution image available of that section, and rotated and cropped it to take a good look:

For the complete orginal file, totally zoomable, with all the metadata and a set of download choices, go here - AS16-P-5401. This is the sort of awesomeness you find deep in the rabbit-holes of the LROC website. The image here is best viewed by right-clicking it and choosing 'view image' or 'open image' in your browser, as it is large.

This image was taken when the sun was 37° above the horizon. (To be precise, at 11:19:13 pm GMT on April 24th, 1972. It was a Monday.) So from the shadows on the east wall it's clear it's inclined almost exactly 37° on average. The wall must be a little steeper in that black puddle where the galleries of Cernan's Promise will be.

The shot shows well the collection of house- to barn-size boulders below the colony site. Perhaps they were created when the large crater just by the rim, inside the indicator square (and nicknamed Teacup), was created. They look like they rolled down the slope, and that jibes with the slight inward dip in the crater rim there, and the flattening at the top of it, to say the impact shook material loose and it pooled down where the crater wall begins to flatten out, against those rocky shelves. All the craters that close to Lalande are younger than it is, otherwise the debris thrown up by the asteroid that created Lalande would have filled them in.

Maybe the layered rocky shelves visible here indicate interfaces between strata with different mineral compositions, or maybe they are just where the rock was flawed due to the particular way it shifted around as it cooled solid, a few billion years ago when this basalt lava sea formed, and the impact blast fractured off the more superficial material there. On average the granular layer is about 1 km deep. 'Granular' refers to chunks of any size, as opposed to rock that is continuous, which is bedrock. Nearer the bottom of that layer the chunks are mostly boulders [1] [2]

How the lunar surface changes with depth. From the Lunar Sourcebook, ch. 4 page 93. This is a 'typical' profile which naturally changes a lot depending on the particular history of an area.

The structure of the ground under Taurus-Littrow, the landing site of Apollo 17. The graphic is from the Moonzoo blog

Map of nighttime soil temperatures by the Lunar Reconnaissance Orbiter Diviner instrument. Each pixel the instrument records is about 200 m across.

Large rocks stores heat better than small grains. The spots that were recorded as being hottest in the image above correspond well to areas where LRO photos show lots of boulders or talus slopes (inclines composed of rocky debris). So the hotspot down the crater wall stays about 30 K warmer (54°F) than the rim at Cernan's Promise overnight, but at its coldest, that warm spot is still about -135°C (-275°F). By noon it is 115°C (240°F).

Lalande Crater east wall
						Lunar Reconnaissance Orbiter image showing detail of debris and strata
Evening image of the Cernan's Promise site by the Lunar Reconnaissance Orbiter.

Outside the lip of the crater is in darkness. About 100 to 200 m inside the lip there is a wavy dividing line where the wall gets steeper, you can tell because its west side is brighter where material has slumped downwards and there are even several landslides. The area between that dividing line and the crater lip is the flattened rim area visible in the third image above. That division exists around the majority of the east and northeast walls. It must correspond to a change in density, meaning a change in composition or an increase in large fragments. Taken together, the photos indicate this division is about 50 or 60 m below the surface outside the rim.

The material that has crumbled is bright because it's fresh, relatively speaking. The faces of those chunks and particles may have been exposed to the sun and sky for less than a billion years. Exposed regolith cracks ever more with the thermal cycle from very hot to very cold every day, and fragments thanks to steady bombardment by very small meteorites micrometers to centimeters in size, and loses its lustre. Fresh material reflects light better. By contrast, dark patches show where the ground is covered by larger chunks - pebbles and small rocks. The gaps between these larger fragments are in shadow so these areas look darker.

Lalande Crater east wall
						below rim Lunar Reconnaissance Orbiter image at noon showing
						flows of debris and depth of stony outcroppings
Noon image near the colony site. Also by the LRO, as are the remaining black and white images. They are from QuickMap. All the LRO images seamlessly laid onto a globe of the Moon. It's for people like us.

The lion's tail shape of the landslide shown at top right of this image is also in the previous image. So, you can see how different the Moon looks at different times of day. Noon is when you can see what shade a material is, instead of the shade value of an area being determined by shadows cast between particles. Suddenly, the long, slender rivulets formed by material rolling down the crater wall are visible. They suggest to me that little patches of stone and regolith crumble occasionally, triggered by the vibrations of a moonquake or an impact in the area, and then roll quite far before coming to rest. Their fluid look indicates a high proportion of small grains in the material slipping down the face.

Things like this are important to consider when you are deciding how to send rovers into this terrain. This is landslide territory. The galleries of Cernan's Promise go right through the middle of it, in fact going through the next gap below the lion's tail one to reduce excavation through those outcroppings that look so rocky. The mass and activity of a rover might not be enough to destabilize the slope, or your extremely expensive rovers might be at serious risk of crushing or burial. It will have to be done carefully.

Those outcroppings are interesting. This image reveals how vertical their faces are, implying the material there is quite cohesive. I don't want to call it rock, because it is too shallow to be a layer of solid rock, and there are no processes on the Moon that produce sedimentary rock. That requires water. Once that occured to me, as i was writing this up, i went on a little mission to find out what that material could be, then. That got nowhere, but led me to other interesting things that were productive. This happens to me all the time. Anyhow, i don't think that material can be supposed to be like rock, but instead like an extra-compacted version of regolith. In particular, the thermal properties of it need to be assumed to be pretty similar to hard-packed regolith, meaning it is more like insulation than a thermal sink.

Map of distribution of thorium on the Moon, by NASA's Clementine probe. Lalande is in the square.

Here we can talk about SaU 169, a meteorite from the Moon that the linked report explains was traced to an origin near Lalande by a rather large team of people who did a rather extensive study on the little thing. The hotspot shows a thorium level of 12 ppm. The meteorite had a level of 33 ppm [1] in the impact breccia [2] that mostly composed it. There is basalt in Italy with 250 ppm of thorium. On Earth that is considered high-grade ore. A low-grade ore has about 50 ppm. Once the bedrock of Lalande is being explored, there could be places with good ore there, concentrations much higher than 33 ppm. That rock would also have the highest concentrations of rare earth elements and uranium.

From the report:

Highly evolved igneous rocks are present on the Moon. Evolved rocks formed from magmas that fractionally crystallized, leaving a residual magma rich in elements that do not readily enter the major rock-forming minerals. The most common class of evolved lunar rock is KREEP, an acronym referring to enrichments (compared to other lunar materials) in potassium (K), rare earth elements (REE), and phosphorus (P). They also contain enrichments in other elements such as zirconium, thorium, and uranium. The formation of evolved magmas involved extensive fractional crystallization in the lunar magma ocean, a huge magmatic system that surrounded the Moon soon after its formation, followed by partial melting of rocks formed from the residual magma. These secondary magmas could have fractionally crystallized further, creating rocks much richer than those observed so far. SaU 169 is without question a KREEP rock. Its thorium (Th) concentration is 33 parts per million in the large impact melt breccia that composes most of the rock. This is higher than all but a few small rock clasts in breccias brought back by the Apollo missions. An interesting feature of the SaU 169 impact melt breccia is that it has a much lower K/Th ratio (137) compared to the average KREEPy rocks (360). This indicates that K and Th, which usually have similar geochemical behavior in magmas, became decoupled from each other, signifying a complicated magmatic history of the lithologies that predated the formation of the impact melt. The rest of the rock is also KREEPy, but does not contain as much Th or REE as does the impact melt breccia, and K/Th is the normal KREEP value.

Breccia refers to rocks made of small chunks glued together by a matrix of another rock type. So, the thorium content in the chunks could be much higher than the mix overall that the tested breccia is made of. The interesting stuff might be in the little bits floating in the sandy brown.

Late morning on the central mountains of Lalande. (On Quickmap, find the really bright impact crater in the middle of the east mountain, this patch is half a kilometer to the northwest.)

Large areas of the central mountains of Lalande are covered in boulders. Each of the 3 big ones at the top is 20 m wide (22 yards). The whole western side of that mountain is blanketed with boulders like this, but the east side has very few by comparison. Why would that be?

This area is here because it shows how jumbled the results were even though what you see here was all created by the same event, which unfolded very quickly. The asteroid struck with incredible force and threw a huge quantity of material outwards. The material that was thrown straight up, came straight back down again and landed here. How long would that have taken, a few minutes? At the same time, the shockwaves that met here at the crater center caused the ground to be pushed up and created these mountains. The lava produced by the heat of the blast didn't pool here, it was above the line of the melt pool. Since there are jagged broken rocks of different materials, as shown by their different tones, light and dark, the stuff that hit the ground here didn't get mixed, and wasn't coated in the lava that was all over. The chunks just hit, broke apart some more thanks to that, and have sat there pretty much exactly the same ever since, for something like 1.5 billion years. They don't even have much dust on them, or the different tones wouldn't show up.

Same exact place as the previous image, at noon.

It looks awfully different at lunar noon, doesn't it? Try the trick of opening each of these images in its own tab by right-clicking and choosing 'View Image' or 'Open in new tab' (depending on which browser you use). Now switch between tabs a few times. The first image exactly overlays the second, everything lines up just the same. But there is no sign at all of that jet-black material in the morning picture. What is that stuff?

It is important to remember that the sun was exactly behind the camera when this image was taken. That maximizes the contrast due to different light absorption of materials. Stuff that is light or white typically is material that broke into chunks with nice, clean flat faces, which reflect light best. Those bits could also be of highlands material, which is largely anorthosite, and that is pale. But the black? Basalt is often very dark stone. And the Moon reflects little light. You don't notice, because you look at it in a black sky, but it is as dark as asphalt. The contrast here could have as much to do with the camera settings as anything else. After looking at a bunch of examples of this phenomenon, such as this, and this, and this, it seems to me these places are where big pieces of solid basalt was smashed into smaller pieces still large and jagged enough that dust slips down their faces, leaving their darkness intact. Or maybe something else is going on. Hard to say without going there. At any rate, if you are looking for the rock with the most KREEP, those ones are maybe the best place to start.

All the clearest images of Lalande stitched together into one continuous piece.

The highest resolution version of this image is 40,000 pixels on a side, making it 1600 Megapixels big. The version here has been cropped to focus on the crater, the full version includes the surrounding terrain out to a distance of about 6 km (4 miles). It took me a month to make it. Towards the end of that month, i realized there was distortion on the floor of the crater that had crept in due to a bunch of details of how it was done which i'd rather not talk about and you'd probably rather not read. I am green with envy at the mainframe computer access and beautifully precise algorithms that allowed NASA to stitch all of the LRO images together so cleanly, almost perfect alignment everywhere at every zoom level. Alright, so in this version the mountains are off by a few hundred meters. It is still a wonderful thing. Definitely. I won't hear otherwise.

For starters, if you are going to build a complete virtual town here with all its infrastructure and industry (and then a city), it really helps to have a highly detailed base map to start with. If you are going to take the very coarse and artifact-ridden LOLA topographical data of this crater and turn it into an accurate 3d model, you need all the images taken when the sun was high, but not at noon when the dazzling contrast prevents you from having any sense of depth. The crater starts to come alive as a real place as its contours are carved digitally into a figure that can me turned, and dived into. When i am able to return to the task and detail it further, i think it will be a real joy. Um, but i'll need two of the very best graphics cards on the market, and to max out my RAM, with faster versions, and maybe overclock the CPU... But that is down the road...

Favorite spots of mine: The two lava 'lakes' in the south wall, where lava pooled in scalloped stone dips. The deep narrow gullies in the north wall. The north spur of the blister-like east mountain, crowded with boulders on its west side. The white boulders strewn down the south wall, the largest 100 m across. Just think, that thing was thrown kilometers high, crashed back down, and it is still in one piece. It would take you several minutes to walk around it.

So, if you wish to see all these things in detail, there is a cropped version here that is 11000 pixels on a side and 11 MB. We won't get crazy with the 200 MB master file.

This model of Lalande is based on LOLA topographical data, the oblique photos taken by Apollo 16, and the above image made from the LRO data, which is laid overtop. Detail will be added to it over time, and it will form the basis of the landscape of the virtual colonies. The photographic texture will be replaced with algorithmic textures that are a good representation of the lunar surface. The largest boulders will be modeled and placed on the model of the ground.